<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .inner1{
            width: 200px;
            flex-grow:10;
        }
        .inner2{
            width: 300px;
            flex-grow: 2;
        }
        .inner3{
            width: 200px;
            flex: 2;
            
        }
        .inner{
            background-color: red;
            height: 200px;
            margin-left: 10px;
            /* 
               三个div，本来的宽度不足以充满父容器
               使用这个属性，就会自动扩大，根据比较，然后充满父容器
               默认值是 0 既不扩大 也不缩小
            */
            flex-grow: 1;
        }
        .outer{
            width: 1000px;
            height: 1000px;
            display: flex;
            border: 1px solid black;
            margin: 0 auto;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="inner inner1">1</div>
        <div class="inner inner2">2</div>
        <div class="inner inner3">3</div>
    </div>
</body>
</html>